1. Field of the Invention
This invention relates to a multilayer structure solid golf ball comprising a core and a cover of at least four layers formed therearound.
2. Related Art
The solid golf ball structures which have heretofore been proposed include multilayer structure solid golf balls comprising a core and a cover which are of multiple layers (see JP-A 8-336617, 8-336618, 9-56848, 9-299510, 11-417, and 11-4916).
One of the purposes of increasing the number of layers in solid golf balls is to obtain a feel equivalent to that of wound golf balls and another is to increase flight distance. In most cases, however, it often occurs that a preference for the feel leads to an unsatisfactory flight distance whereas the satisfaction of flight distance leads to a poor feel. Also, most prior art proposals mainly target golf players with a high head speed capability. Thus, there is a desire to have a golf ball which offers a satisfactory flight distance and a pleasant feel even when hit at low head speeds.
An object of the present invention is to provide a multilayer solid golf ball which offers a satisfactory flight distance and a pleasant feel not only when hit at high head speeds, but also when hit at low head speeds.
To achieve this and other objects, the present invention provides a golf ball as defined below.
(1) A multilayer solid golf ball comprising a core and a cover of four layers, characterized in that a first layer of the cover enclosing the core has a Shore D hardness of at least 55, a second layer of the cover enclosing the first layer has a Shore D hardness of up to 45, the difference in hardness between a third layer of the cover enclosing the second layer and the second layer is at least 5 Shore D units, and a fourth layer of the cover enclosing the third layer is made harder than the third layer.
(2) The solid golf ball of (1) wherein the first layer of the cover has a Shore D hardness of 55 to 70, the second layer of the cover has a Shore D hardness of 10 to 45, and the third layer of the cover has a Shore D hardness of 25 to 50.
(3) The solid golf ball of (1) or (2) wherein the core has a diameter of 26 to 35 mm, the core at its surface has a Shore D hardness of at least 40, and the fourth layer of the cover has a thickness of 0.5 to 3.0 mm.
(4) The solid golf ball of any one of (1) to (3) wherein the second and third layers of the cover each are formed of at least one member selected from the group consisting of polyester resins, polyurethane resins, and thermoplastic polyamide elastomers.
(5) The solid golf ball of any one of (1) to (4) wherein the fourth layer of the cover is formed of an ionomer resin.
Making extensive investigations in the light of the above object, the inventor has found that by forming a cover from the above-described four layers, a difference in hardness can be established between the intermediate second and third layers of the cover. This smoothens the change of hardness for thereby improving resilience and feel and optimizing the amount of deformation. Consequently, there is obtained a ball which is highly resilient although it is soft.